December 9: Christmas Tree worm was discovered (1987)

A screen capture of the infected
computer by Christmas Tree worm

Christmas Tree was the first widely spread disruptive computer worm, which paralyzed several international computer networks including BITNET, EARN, IBM VNET in December 1987. It was written by a student at TU Clausthal in Germany, in the Rexx script language with EXE extension. This worm asked the user to type CHRISTMAS in the command line and if the user typed the text, it then drew a Christmas tree as text graphics and sent itself to every entry stored in the email contacts file. This harmless looking computer code caused a significant disruption to the public network. It made us think of how the benefits of the network can be adversely abused to defeat the network.